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Thursday, November 14, 2013

Scientists create another invisibility cloak

A clocking device is created

Who didn’t wish he/she had an invisibility cloak after reading Harry Potter evade Professor Snape’s detection in precarious situations? Well, that cloak remains in fantasy books, but scientists are closer to making it a reality with a “broadband” invisibility cloak capable of hiding object over a wide range of frequencies.

Not as wide reaching and far more plausible than the Harry Potter’s cloak, the old models of cloaks work by bending microwaves around objects. The first successful one in 2006 concealed a small copper cylinder.

The best designs so far are only capable of hiding objects under specific wavelengths of microwaves and light. According to some US physicists those invisibility cloaks even make objects even more visible under different frequencies.

So these physicists devised a new ultra-thin electronic system, explained in Physical Review Letters.

“Our active cloak is a completely new concept and design, aimed at beating the limits of [current cloaks] and we show that it indeed does,” said Andrea Alu, a professor from the University of Texas at Austin. “If you want to make an object transparent at all angles and over broad bandwidths, this is a good solution. We are looking into realizing this technology at the moment, but we are still at the early stages.”

The team looked at the three most common types of cloaks, called “passive” cloaks for not needing electricity. The three times were a plasmonic, mantle and transformation-optics cloak.

Over the whole electromagnetic spectrum, these cloaks scatter more waves than the object they cover. Because of that, the team found that current passive designs could not make an object completely invisible.

“When you add material around an object to cloak it, you can’t avoid the fact that you are adding matter, and that this matter still responds to electromagnetic waves,” said Alu.

So what his team decided was to work with “active” cloaking technology, technology that required electricity to make objects invisible. This cloak would be thinner and lighter and would make the object “disappear” at a much broader range of frequencies than current cloak designs.

While far from the “perfect” cloak we envision for sneaking out of work early, David Smith, professor at Duke University who was part of the team that developed the 2006 cloak, says the new cloak still has use.

“To most people, making an object ‘invisible’ means making it transparent to visible wavelengths. And the visible spectrum is a tiny, tiny sliver of the overall electromagnetic spectrum,” he told BBC News. “So, this finding does not necessarily preclude the Harry Potter cloak, nor does it preclude any other narrow bandwidth application of cloaking.”